The present invention relates to tantalum capacitors and more particular to wet tantalum capacitors using liquid electrolytes.
Wet tantalum capacitors have applications as a filter capacitor for power supplies. Typical of such capacitors are tantalum capacitors which utilize a silver liner inside a steel shell. Colloidal graphite is applied to the interior surface of silver liner and the silver-graphite serves as the cathode of the capacitor. The colloidal graphite is used to increase the capacitance of the cathode system.
The design has several major drawbacks which limit its applications or its performance life. If the finished capacitor is subjected to a reverse voltage of 1 volts dc, silver will dissolve in the electrolyte and electro-deposit on the surface of the anode. This will cause high dc leakage or a short circuit when voltage is applied in the correct polarity.
And when it is used under high ripple current conditions, such as a filter capacitor for a power supply, the colloidal graphite can become dispersed in the electrolyte. If the dispersed graphite makes intimate contact with the anode it will cause high dc leakage or a short circuit condition.